will it eliminate inventory entirely. No.

Will it mean large companies can offload a warehouse full of plastic replacement widgets and get the end consumer to pay for the secire digital file and also pay for their own manufacturing materials ?

Oh hell yeah. Just as soon as a secure and time limited 3d file hits the market alongside a self levelling, idiot proof 3d printer.
And features it will have to have: automatic model removal from the build plate, automatic filament loading from a custom cartridge.
No complicated controls. All settings to be incorporated in the actual model file. So all the user does is download the file and punch the big green button that says: GO !

Give it 5-10 years.